There are a number of automated open relay tests available. Alternately, we can also manually perform the test for an open relay.
There are several automated open relay testers. We need to use a telnet session to access and use their services. The best-known relay tester is relay-test.mail-abuse.org
.
To use this service, we enter the following command at the command prompt of the mail server we are testing:
telnet relay-test.mail-abuse.org
An example session follows:
$ telnet relay-test.mail-abuse.org
Trying 168.61.4.13...
Connected to cygnus.mail-abuse.org.
Escape character is '^]'.
Connecting to 999.888.777.666 ...
<<< 220 domain.com ESMTP My_MTA
>>> HELO cygnus.mail-abuse.org
<<< 250 domain.com
:Relay test: #Quote test
>>> mail from: <spamtest@mta.domain.com>
<<< 250 Ok
>>> rcpt to: <"nobody@mail-abuse.org">
<<< 554 <nobody@mail-abuse.org>: Relay access denied
>...